Information regarding the physiological parameters of a subject is important in a variety of contexts and applications, including for healthcare, military, sports, education, adaptive learning, and personal fitness purposes. For example, in psychophysiological research, it is known that the arterial pulse amplitude and rate and respiration of a subject can vary according to the behavioral, emotional, and cognitive challenges presented to the subject. In clinical settings, the condition of a patient may be determined by the measurement of beat-to-beat indices of rate and amplitude of the arterial pulse and breath-to-breath indices of respiration. In intelligence, security, and law enforcement communities, information regarding the physiological parameters of a subject may be useful to achieve a variety of goals.
A variety of devices and methods have been developed by which the physiological parameters of a subject, such as a human subject, can be measured. One such well known group of such devices requires direct contact with the subject in order to obtain the desired information. For example, the stethoscope is an acoustic medical device that is applied to the body of a subject for auscultation purposes, that is, listening to the lung and heart sounds, to the sound of intestines, to the flow of blood in arteries and veins, and other internal sounds of the subject's body. The stethoscope may be used with a sphygmomanometer, another device that is applied to the body of the subject and is commonly used for measurements of blood pressure. Another device, a pulse oximeter is configured to be placed on the fingertips or earlobes of a subject in order to monitor pulse and hemoglobin oxygenation levels. The pulse or heart rate of a subject can be detected and monitored with the use of an electrocardiography (“ECG”) device. Such devices detect and amplify the electrical changes that the beating heart produces on the skin of the subject through the use of electrodes affixed to the skin of the subject to which has been applied a gel.
Besides having to be applied to the body of the subject in order to obtain the desired information, there are a variety of other limitations associated with such known measurement devices and methods. One is that in all cases the subject must be located within a distance of the device so that at least the probe portion of it can be applied to the body of the subject. Another is that certain known devices require that some material be applied to the body of the subject before contact of the probe with the body is made. For example, with an ECG device, gel must be applied to the body of the subject before the electrodes are affixed to the body. A material such as this gel may cause irritation of the skin of the subject. Such known systems and methods may provide also a limited range of information that is often qualitative, may be inconvenient for both the subject and the operator, and by their use the physiological parameter(s) that are being measured may be affected.
Other devices have been developed for the estimation and monitoring of a subject's heart rate which do not require contact with the subject's skin. These non-contact devices are based on the recognition that the beat of the heart sends a pulse wave through the subject's body. The wave produces slight changes in the blood vessels beneath the skin of the subject. The small changes in the blood vessels can produce changes in the light that is reflected from the skin. By obtaining a color image of the skin of the subject, and analyzing the images for changes in light reflectance, the pulse of the subject can be determined. Devices that estimate the pulse of a subject based on the light reflected from the skin of the subject typically do so by taking a sequence of multiple images of the subject and collectively analyzing and comparing the entire group of images to obtain an estimation of the subject's heart rate.
Many known non-contact heart rate estimations/monitoring systems and methods have a number of limitations associated with them. One is that they typically require that images be captured of a subject over a period of time. The need to capture such a series of related images adds to the amount of time that is needed in order to conduct and complete the analysis of interest and make a determination regarding the heart rate of the subject. The subject may move or the lighting of the subject may change during the period in which the images are captured. Such changes in the subject and the context in which the images of the subject are taken add to the complexity of the processing needed to obtain the information that is sought. Also, as the number of images that are taken increases, the amount of data that must be gathered, recorded and processed in order to make the determination increases. For example, if a video recording is taken of a subject for 60 seconds at 60 frames per second, and each of the frames has a region of 300 by 300 pixels, with separate data collected for certain colors—for example, red, green, and blue—the data integer values equals 972 million. Expanded resources are needed to receive and record this amount of data. Handling and processing this amount of data is time consuming and increases the chance that error will occur.
Accordingly, there exists a need for a noncontact technology capable of detecting human physiological parameters that provides accurate information, is quick and efficient, and convenient to use for both operator and the subject. The present invention satisfies the demand.